Morphology and the structure of quasicrystal phase in as-cast and melt-spun Mg-Zn-Y-Zr alloys

Abstract

During recent years, many researchers have investigated the experimental and theoretical aspects of quasicrystal materials. In some Mg alloys (Mg[sub 32]Al[sub 17]Zn[sub 32], Mg[sub 32](Al,Zn)[sub 49], Mg[sub 32] (Al,Zn,Cu)[sub 49], Mg[sub 4]CuAl[sub 6] and Ga[sub 16]Mg[sub 32]Zn[sub 52]), icosahedral quasicrystals (IQC) have been found. However, most of the quasicrystals in these alloys were formed under a rapid solidification condition. In the recent study on Mg-Zn-(Zr,Y) as-cast alloys, the authors identified a new Mg-rich and a Zn-rich IQC by X-ray diffraction (XRD) and electron microscopy (EM). The discovery of Mg-Zn-Y IQC is of interest because it formed in an as-cast ingot and did not contain the element Al, which is the major constituent of nearly all IQC forming alloys reported. Also, analyses on IQC in as-cast and RS Mg alloys with the composition have not previously been carried out. In this paper, TEM and XRD investigations were completed on IQC formed in a Mg-Zn-Y-Zr cast ingot and melt-spun ribbons for microstructure comparison.